The invention encompasses a system for the filtration of media by means of a membrane structure consisting of, for example, membrane channels or membrane discs. Such systems are utilized in the most diverse sectors of industry, for example in the food industry or the paper industry.
In the case of disc-shaped membrane structures, the medium to be filtered is introduced on one side of the circumference of the disc, and the retentate is withdrawn from the opposite side. The permeate is removed after passage through the membrane.
A crucial requirement of a membrane system is its highly precise separation. The undesirable components should be separated as completely as possible from the desired components. A further requirement is a high permeate delivery in quantity per unit time for a given space requirement. Furthermore the energy consumption plays an important role.
The permeate delivery, or output of membrane systems, drops off after a certain period of operation, as a result of the deposition of solids on the membrane. In order to prevent or reduce this effect, countermeasures have been implemented. So, for example, it has been attempted to keep the membrane surface free of deposits by installing an impeller above the membrane surface, so as to keep the medium above the membrane in a state of turbulence. Similarly, scrapers have been employed to scrape deposits off the membrane surface.
These measures are, however, not entirely satisfactory.
The invention has the objectives of providing a system of the type described above, structured in such a Fray that the separation precision is maintained over a longer period of time, furthermore, a durable, high throughput can be achieved, the space requirement can be kept at a minimum, and the energy consumption is reduced in comparison to known systems.
These objectives are achieved by the features of the present invention.
According to the invention, the membrane discs of one membrane pack protrude into the spaces between consecutive discs of the second membrane pack (Dummy Pack). Viewed from above, this results in a degree of coverage or overlapping of the discs of one pack by the discs of the other pack. If the discs rotate, the radially external area of one disc will overlap the radially internal area of the other disc, so that the relative speed between two adjacent plates is made up of a high and a low speed. The relative speed between two plates is, therefore, essentially constant in the radial direction. This has a positive effect on the throughput, and consequently the energy consumption.
The invention comprises two main embodiments.
The first embodiment is to use a primary membrane pack which comprises a hollow shaft, and a secondary pack with a shaft that need not be hollow, and with discs that have a sealed outer surface.
A drive system serves to rotate the shafts of each of the packs. The packs can be rotated in a same direction as one another, in opposite directions from one another, and they can be oscillated. During rotation, the discs of the secondary pack run across the membrane discs of the primary pack. By this action, they cause agitation of the medium in the system and prevent deposition of substances on the surfaces of the membrane discs.
The second embodiment utilizes hollow discs and a hollow shaft for the secondary pack. The inner spaces of the hollow discs are connected to the space in the hollow shaft.
In one execution of the stated second embodiment the medium to be treated can be fed into the inside of the hollow plates of the secondary pack via the hollow shaft The discs of the secondary pack are equipped with openings or nozzles, which are directed against the surface of the membrane discs of the primary pack. So that the medium impacts on the membrane discs with a certain over-pressure and a certain flow velocity, which improves the performance of the entire system.
In any case, the discs of the secondary pack can have raised sections or elevations on their outer surfaces, so as to cause agitation of the medium contained in the apparatus, thereby reducing the danger of materials setting out on the membrane discs.